Metal-organic frameworks (or MOFs), which are hybrid materials composed from organic linkers and metal ions, demonstrate excellent properties for gas purification, separation, and storage. In addition, nanoporous MOF thin films are particularly useful in chemical sensing due to their tunability and structural diversity. Despite the high potential of sensors using MOFs, the lack of a highly sensitive and specific signal transduction method has limited their implementation industrially.
Infrared absorption sensors play pivotal roles in analytical chemistry, allowing the quantitative detection of small amounts of molecules and the identification of molecular structures and conformational states. Instrumentation used to detect IR absorption, however, is expensive and not easily transported. While there have been instances of using fiber-optic sensors for chemical sensing, these systems have failed to exhibit utility in particular sensing applications, such as gas sensing, due to low molecule density or high selectivity to a particular gas species of interest within complex gas mixtures. Additionally, most gases do not have fundamental vibration bands at NIR regions; therefore, there has been little success in adopting near-infrared (NIR) optical fibers and optoelectronic devices to detect gases.
Conductive MOFs may be useful for electronic devices and reconfigurable electronics, including sensors. Gold substrates are conventionally functionalized by thiol-based self-assembled monolayers (SAMs), and are used to nucleate MOFs and subsequently oriented film growth. However, the use of these SAMs is limited due to their thermal and chemical stability, as well as their insulating nature, which can result in poor electrical contact. There is a need in the art for improved sensors that address these limitations.